Method for preparing for a change of material in an extrusion device for a film machine

ABSTRACT

The above object is solved by means of a method comprising the features as described herein as well as an extrusion device comprising the features as described herein. Further features and details of the invention follow from the depending claims, the description and the drawings. It goes without saying that features and details, which are described in connection with the method according to the invention, shall thereby also apply in connection with the extrusion device according to the invention and in each case vice versa, so that, with regard to the disclosure, reference is or can always be mutually made, respectively, to the individual invention aspects.

The present invention relates to a method for preparing for a change ofmaterial in an extrusion device for a film machine as well as to acorresponding extrusion device with the option of carrying out such amethod.

It is basically known that material changes have to be carried out inextrusion devices for film machines. For example, different products,which differ in particular with regard to their used formulas and thuswith regard to their used material compositions, can thus be produced ona film machine. To be able to run different material compositions on aproduction machine, the different feedstocks need to be adapted orchanged, respectively. In other words, a change of material can becarried out between the materials of an application formula and thematerials of a subsequent formula.

A disadvantage of the known solutions is that the change of material iscarried out at the end of the order, thus when the desired quantity ofproducts of a feedstock or of an application formula, respectively, hasbeen produced. At that point in time, the respective feedstock islocated in an extrusion device in a feed unit for feeding this feedstockto the extruder. To be able to carry out the change of material, thefeedstock needs to now be discharged manually from this feed unit andneeds to be replaced by the subsequent feedstock, which can beidentified as subsequent material at that point in time. As a result,the entire material quantity of feedstock, which is still located in thefeed unit at that point in time, needs to be discharged, and isconsidered to be waste.

Moreover, the discharge of the feedstock from the feed unit is atime-consuming process, because it is necessary to wait until the entirequantity of feedstock has discharged from the feed unit, in particularby means of gravity conveyance.

It is the object of the present invention to at least partiallyeliminate the above-described disadvantages. It is in particular theobject of the present invention to reduce the time for the change ofmaterial in a cost-efficient and simple manner and to preferably alsoreduce the amount of waste.

The above object is solved by means of a method comprising the featuresas described herein as well as an extrusion device comprising thefeatures as described herein. Further features and details of theinvention follow from the depending claims, the description and thedrawings. It goes without saying that features and details, which aredescribed in connection with the method according to the invention,shall thereby also apply in connection with the extrusion deviceaccording to the invention and in each case vice versa, so that, withregard to the disclosure, reference is or can always be mutually made,respectively, to the individual invention aspects.

A method according to the invention serves the purpose of preparing achange of material in an extrusion device for a film machine. Such anextrusion device is equipped with at least one feed unit for feedingfeedstock to an extruder. The method according to the inventioncomprises the following steps:

-   -   predetermining an end of a production order of an extrusion        device,    -   specifying a reduced changing filling level for the at least one        feed unit,    -   maintaining the filling level of the at least one feed unit at        the reduced changing filling level for the further production        with the extrusion device.

According to the invention, the production order is thus now monitoredand is predetermined with regard to an expected end. This can take placefor example by calculating the remaining running time based on theresidual quantity of the production order. It is also conceivable,however, for the predetermining to include a manual input by theoperating personnel of the extrusion device. A control unit of anextrusion device, on which a method according to the invention can becarried out, is now able to identify the end of a production order inthis way and to use it as the basis for the further regulation of theprocess. The production order means in particular that a product, whichis ready for sale, of a film is produced during the production order.The production order has to be differentiated from the intermediateperiod or the changing period, respectively, between two productionorders, in which the subsequent formula is not yet produced and in whichthe application formula is also not in the process any longer. Thischanging period thus leads to a waste material, which cannot beidentified as product, which is ready for sale.

If a control unit now identifies the end of a production order whencarrying out a method according to the invention, the specification of areduced changing filling level for the at least one feed unit can bemade on this basis. A changing filling level is thereby in particularreduced with regard to the regular operating filling level inside therespective feed unit. To ensure that the risk that the extruder drainsduring operation is reduced to a minimum during operation, relativelylarge quantities of feedstock are typically kept available in the feedunit with a correspondingly large buffer effect. This prevents that adraining of the extruder occurs even in the case of mechanicalmalfunctions of a supply device into the feed unit. As soon as theproduction end or the end of the production order, respectively, hasbeen predetermined, a reduced changing filling level can now however bespecified. This thus has the result that the filling level inside therespective feed unit drops during the period of the further production,until the corresponding changing filling level is reached as reducedchanging filling level, based on the operating filling level. Accordingto the invention, this filling level of the at least one feed unit isnow maintained at the reduced changing filling level for the furtherproduction with the extrusion device. This means that, starting at thatpoint in time, the further operating process is now carried out with alower buffer effect. Due to the fact, however, that this is a point intime, at which the end of the production order is already predetermined,a machine operator is typically also present at the location of theproduction. It is thus no longer necessary to provide the high buffereffect, because the machine operator can now react flexibly and quicklyin the case of an error.

Maintaining the filling level at the reduced changing filling level canthereby take place in a constant manner as well as in batches. Thisdepends in particular on the type of subsequent conveyance. So-calledbatch processes are known, in the case of which a refilling from a feedcontainer to a down pipe or a weighing funnel can in particular takeplace in batches or continuously. It is also conceivable that afollow-up of feedstock into the feed unit is provided with the help of asuction conveyance. In the case of a maintaining of the filling level inbatches, a refilling thrust is thus made exactly when the filling levelreaches the reduced changing filling level. The maintaining of thefilling level is to thus in particular be understood in such a way thatthis filling level does not fall below or only falls below the reducedchanging filling level by a minimal and predefined amount, for exampleby approximately 10%.

The above-described method is carried out until the actual change ofmaterial is initiated. An extended production can moreover also becarried out in this way on the basis of this method with the reducedchanging filling level, if this is a flexible desire of the machineoperator.

A feed unit can thereby preferably be equipped as weighing funnel, downpipe and/or feed container, wherein a suction conveyance or a batch feedfor the refilling functionality of the feed unit can be provided. A filmmachine can be a blown film production or also a different type of filmproduction, in particular a so-called cast film production.

A method according to the invention is associated with severaladvantages. The quantity of feedstock, which is located in therespective feed unit, is significantly reduced with regard to thereduced changing filling level, in particular at the time the change ofmaterial starts. This means that a smaller quantity of feedstock needsto be removed from the feed unit for carrying out the change ofmaterial. This has in particular two significant effects. On the onehand, the expenditure of time for discharging the residual feedstock,which is reduced in this way, is reduced significantly. For the casethat the discharged feedstock is material, which cannot be recycled, thewaste or scrap, respectively, which is created therewith at the sametime, is reduced significantly therewith.

It may be advantageous when, in the case of a method according to theinvention, the filling level of the at least one feed unit is increasedin batches, in particular in a single refilling thrust, when the fillinglevel falls below the changing filling level. This is to be understoodin such a way that in particular no continuous subsequent conveyancetakes place, but that an in particular defined refilling quantity is infact always introduced into the feed unit with the help of refillingthrusts. Provision can thus be made for example for a common suctiondevice, which provides suction thrusts for all feed units with the helpof a low pressure and a single pump. A feed unit can thus always beoperated with a refilling thrust or a plurality of refilling thrusts. Alimitation to in particular a single refilling thrust has the resultthat the fluctuation prior to the refilling thrust and after therefilling thrust, and thus the amplitude, at which the actual fillinglevel fluctuates in response to carrying out a method according to theinvention, is reduced. In the case that the change of material startsexactly when a refilling push has just been introduced, the quantity offeedstock, which is to be maximally discharged in this way, is reducedsignificantly. A fluctuating filling level and simultaneously acorresponding combination of a residual buffer of the feedstock and thereduced changing filling level thus results.

It is advantageous when, in the case of the embodiment of the aboveparagraph, the increase of the filling level in batches is made with asingle refilling thrust, which refills less feedstock than an operatingthrust during the normal production operation of the extrusion device.This means that substantially a complete refilling of the feed unit toan upper maximum filling level has to take place during the normalproduction operation, in order to continue to provide the maximum buffereffect. To prepare for the change of material, it may now beadvantageous for a method according to the invention to reduce thisoperating thrust to a refilling thrust. This is ensured in particular inthat the time period, during which suction takes place, thus theduration of the refilling thrust, is reduced as compared to the durationof the operating thrust, for example in the case of a suction conveyor.As a result, not only a reduction of the number of the refillingthrusts, but in fact also a reduction of the quantity per refillingthrust can be capable of being attained in response to an increase ofthe filling level in batches. An even further reduced changing amplitudeis thus attained between the actual filling level and the changingfilling level, so that a shortened refilling time for this refillingthrust can moreover be expected as well. A slighter blockade for otherfeeds thus takes place, so that a smaller buffer can also be used inthis way for the other feed units.

It is a further advantage when, in the case of a method according to theinvention, the volume and/or the weight of feedstock, which correspondsto the changing filling level in the feed, has a refilling ratio ofbetween 0.5:1 and 10:1 with the volume and/or the weight of thefeedstock of a refilling thrust. This thus means that a definedspecification of the relation between the refilling and the remainder offeedstock is specified. A refilling ratio of between 0.5:1 and 5:1 ispreferred, a refilling ratio of between 1:1 and 4:1 is particularlypreferred. In individual cases, it may be preferred, when the refillingratio is in the range of between 1.5:1 and 2.5:1. In particular in thecase of ranges, in which a small refilling thrust is sufficient tomaintain a corresponding quantity of feedstock at changing fillinglevel, are thereby preferred. On the one hand, an absolute reduction ofthe residual filling level inside the feed unit as a result of thereduced changing filling level is thus advantageous. On the other hand,a reduction of the corresponding amplitude is expedient, in order toobtain the smallest possible exceeding of the changing filling level forthe most negative case of the change of material, thus the start of thechange of material directly after a refilling thrust.

It may be a further advantage when, in the case of a method according tothe invention, a minimal filling level, which is smaller than thechanging filling level, is specified at a defined point in time prior tothe end of the production order, and when the filling level of the atleast one feed unit is maintained above the minimal filling level forthe further production with the extrusion device. This is thus aso-called two-stage filling level process. After initiating a methodaccording to the invention, it is thus verified, whether a minimalfilling level may be expedient. This can be direct as well as indirect.A control unit is thus brought into a changing state according to theinvention either manually or automatically, and will approach thecorresponding changing filling level. As soon as the operating personnelis in the vicinity and desires to start the change of material, thebuffer effect inside the respective feed unit can be reduced evenfurther, because the change of material is imminent. Acomponent-specific selection can thus be made in manual direct manner orby means of a defined specification in an automatic manner, for examplewith the help of a defined point in time of approximately five minutes.As a result, an even further reduction of the filling level to theminimal filling level takes place and the maintaining function of thefilling level for the respective feed unit is now carried out for thisminimal filling level. This, however, is only sufficiently safe, whenthe operating personnel is in fact in the vicinity and if the last phaseimmediately prior to the actual change of material now does prevail.

It is a further advantage when, in the case of a method according to theinvention, provision is made for at least two feed units, wherein aspecific changing filling level is specified for each feed unit in theextrusion device.

The respective feed unit can also be identified as component or materialcomponent. Every material component in the respective formula is thusspecific with regard to the used quantity and the associated conveyingspeed. If, for example, a material component, which takes effect onlywith a very small percentage in the entire application formula, isstored in a feed unit, the corresponding conveying speed for this feedunit will be very low. If, in contrast thereto, a different materialcomponent is used in a different feed unit with a high volumepercentage, a high conveying quantity will provide a correspondinglyquick outputting of this material from the feed unit there. As afunction of the different outputting speeds, different changing fillinglevels can now be provided. In the case of a lower outputting speed, asimilar buffer effect can thus also be attained with a significantlysmaller changing filling level, than is the case in the case of a highoutputting speed for a correspondingly other feed unit. Amaterial-specific reduction of the time or of the material,respectively, thus takes place and thus an option for a furtheroptimization for carrying out the method according to the invention.

It is also advantageous when, in the case of a method according to theinvention, the lowering time, which is required by the furtherproduction for lowering the filling level to the changing filling level,for the at least one feed unit is determined after predetermining theend of the production order, and when the reduced changing filling levelis specified, when the remaining time to the end of the production orderis equal to the lowering time. This means that when the production orderis predetermined with regard to its end, it is simultaneouslypredetermined, how long the lowering of the filling level will take as afunction of the actual production parameters. The lowering time for therespective feed unit is thus longer, when the conveying speed for thisfeed unit is low, and is shorter, when the conveying speed for this feedunit is quick. As soon as the remaining time to the end of theproduction order is now equal to this lowering time, the specificationof the reduced changing filling level specifically for this feed unitstarts. Columns, which drop at different speeds, thus follow, whereinthe lowering of the respective column of a feed unit can start atdifferent points in time. It goes without saying that the embodimentcondition, namely that the remaining time is equal to the lowering time,is to be understood to be a technically fluctuating range. A toleranceof up to +10% can thus be possible in response to the triggering due tothe equality between lowering time and remaining time. It goes withoutsaying that provision can also be made for residual buffers, so that allfeed units are at the desired changing filling level and thus in thepreparatory operation, for example five minutes prior to or also afterthe end of a corresponding production order.

It is further advantageous when, in the case of a method according tothe invention, a filling level signal, which includes in particular atleast one of the following pieces of information, is received by acontrol device in order to maintain the filling level:

-   -   weight of an at least partially filled weighing funnel of the at        least one feed unit    -   filling level in a weighing funnel of the at least one feed unit    -   filling level in a down pipe of the at least one feed unit    -   filling level in a feed container of the at least one feed unit

The above enumeration is not a conclusive list. It goes without sayingthat a filling level signal can be received by a control device, and canalso have two or more pieces of information. Different signals ordifferent sensors, restively, which provide the desired signals, arethus conceivable.

An extrusion device comprising an extruder and at least one feed unitfor feeding feedstock to the extruder is also a subject matter of thepresent invention. Such an extrusion device has a filling level sensorfor determining the filling level in the at least one feed unit.Provision is further made for a control device for predetermining an endof a production order of an extrusion device, a specifying of a reducedchanging filling level for the at least one feed unit, and for amaintaining of the filling level of the at least one feed unit at thereduced changing filling level for the further production with theextrusion device. It is advantageous, when the control device isembodied for carrying out a method according to the invention. Anextrusion device according to the invention is thus associated with thesame advantages, as they have been discussed in detail with reference toa method according to the invention.

Further advantages, features and details of the invention follow fromthe description below, in which exemplary embodiments of the inventionare described in detail by referring to the drawings. The featuresmentioned in the claims and in the description can thereby besignificant for the invention, in each case alone or in any combination.Schematically:

FIG. 1 shows an embodiment of an extrusion device according to theinvention,

FIG. 2 shows the embodiment of FIG. 1 during the lowering of the fillinglevels,

FIG. 3 shows the embodiment of FIGS. 1 and 2 with filling levels atchanging filling level,

FIG. 4 shows the embodiment of FIGS. 1 to 3 during a refilling thrust,

FIG. 5 shows the embodiment of FIGS. 1 to 4 during a minimal fillinglevel,

FIG. 6 shows the filling level course in a schematic illustration and

FIG. 7 shows an alternative embodiment of an extrusion device.

An extrusion device 10 according to the invention is discussed in moredetail by means of FIGS. 1 to 5. In the case of this embodiment, saidextrusion device is equipped with two feed units 20 in a schematic andexemplary manner. Each of these feed units 20 has a storage container26, a down pipe 24 and a weighing funnel 22. In the normal operatingmode, the respective feed unit 20 is completely filled with feedstock Ehere, so that FIG. 1 substantially represents an operating filling levelBF for the feedstock E.

As soon as a request to change the material is identified, a controldevice 40 can carry out a corresponding method according to theinvention. As a result, the production end is now predetermined and acorresponding lowering of the individual filling levels F is carried outin the feed units 20 by means of the predetermination, in particular incorrelation with the lowering time AZ and a remaining time RZ for theproduction end. A snapshot during these dropping filling levels F isillustrated in more detail in FIG. 2.

The lowering of the filling levels F is ended, when the situationaccording to FIG. 3 has been reached. In order to identify thissituation, provision is made here for filling level sensors 42. In thecase of the right feed unit 20, this filling level sensor 42 is embodiedas inductive sensor, which can identify exactly one filling level. Dueto the fact that provision is in each case made in the case of the leftand right feed unit 20 for a weighing funnel 22, a filling level sensor42 can now also be coupled to this weighing system in the case of theleft feed unit 20. A further changing filling level WF can thus bespecified here via a weight evaluation. As soon as the respectivefilling level F has now reached the corresponding changing filling levelWF, the control device 40 will try to maintain the changing fillinglevel WF. A falling below is to be avoided thereby or a maximum fallingbelow of approximately 10% is to be maintained. At the point in time asshown in FIG. 3, a refilling will now take place inside the feed units20. This takes place in particular in batches, for example with the helpof a single refilling thrust. The filling level F in the two feed units20 thus now increases significantly above the changing filling level WFagain. This situation is maintained until the change of material is nowin fact carried out.

FIG. 5 shows that a further reduction and thus a second reduction of thefilling level F can now also take place in particular on the basis of amanual input by a machine operator. A minimal filling level MF is thusspecified here, so that the feedstock E, which remains in the respectivefeed unit 20, is reduced even further. As can be seen in FIGS. 1 to 5,the residual quantity of the feedstock E is thus reduced, which needs tobe considered in response to the change of material, which is to becarried out. On the one hand, the waste or the scrap, respectively, ofdischarged residual material of the feedstock E is thus reduced. On theother hand, the period, which is necessary for discharging the residualfeedstock E from the respective feed unit 20, is reduced significantly.

FIG. 6 shows, schematically, how a filling level F can develop overtime. On the top left, the filling level F thus starts at an operatingfilling level BF and thus with filled feed units 20. During the courseof the production, the filling level F also drops here, but a refillingthrust effects a refilling to the operating filling level BF again andagain. This leads to a corresponding saw tooth characteristic on the topleft in FIG. 6. As soon as the production end has been predetermined,the method according to the invention can start, so that the fillinglevel F now drops. A corresponding period, which is equal to orsubstantially equal to the remaining time RZ to the end of theproduction order in this embodiment, needs to in particular beconsidered thereby. As soon as the filling level F has now reached thechanging filling level WF, a falling below of this changing fillinglevel WF is prevented by means of a refilling thrust. The system ismaintained in this situation, so that a saw tooth profile, whichprevents the filling level F from falling below the changing fillinglevel WF or reduces it to a minimum, now also forms on the bottom right.

FIG. 7 shows an alternative embodiment of an extrusion device 10. Withregard to the advantages described according to the invention, saidextrusion device is based on the embodiment of FIG. 1, but differs inthe refilling function. Provision is thus made here for a so-calledbatch process for the refilling. The feed container 26 is equipped withseparate volumes, so that each volume of the feed container 26 can beunderstood to be a feed unit 20. Components in the form of the down pipe24 and of the weighing funnel 22 arranged therebelow are thus commoncomponents of the different feed units 20. Provision is made below theweighing funnel 22 for a mixing funnel, in particular comprising a mixerdrive, which allows for a homogenization prior to entering the extruder.

The above discussion of the embodiments describes the present inventiononly in the context of examples. It goes without saying that individualfeatures of the embodiments, if technically expedient, can be combinedfreely with one another, without leaving the scope of the presentinvention.

LIST OF REFERENCE NUMERALS

-   10 extrusion device-   20 feed unit-   22 weighing funnel-   24 down pipe-   26 feed container-   28 dosing screw-   30 extruder-   40 control device-   42 filling level sensor-   E feedstock-   BF operating filling level-   WF changing filling level-   MF minimal filling level-   F filling level-   AZ lowering time-   RZ remaining time-   t time

The invention claimed is:
 1. A method for preparing for a change ofmaterial in an extrusion device for a film machine comprising two feedunits for feeding feedstock to an extruder, comprising the followingsteps which are carried out by a control device as soon as a request tochange the material is identified: monitoring a production order andpredetermining an end of the production order of the extrusion deviceautomatically by calculating a remaining production time based on aremaining quantity of the production order, specifying a reducedchanging filling level for each feed unit, and maintaining a fillinglevel of each feed unit at the reduced changing filling level for afurther production with the extrusion device, wherein the control deviceidentifies the end of the production order and uses the end of theproduction order as a basis for further regulation of the method, andthe control device makes the specification of the reduced changingfilling level for each feed unit on this basis, wherein the changingfilling level is reduced with regard to a regular operating fillinglevel inside each respective feed unit, wherein a lowering time, whichis required by the further production for lowering the filling level tothe changing filling level, for each feed unit is determined afterpredetermining the end of the production order, and the reduced changingfilling level is specified, when a remaining time to the end of theproduction order is equal to the lowering time, wherein the film machinecomprises two feed units, wherein a specific changing filling level isspecified for each feed unit of the extrusion device, and wherein alowering of a respective column of a corresponding feed unit of the twofeed units starts at different points in time, if columns of the twofeed units drop at different speeds.
 2. The method according to claim 1,wherein the filling level of each feed unit is increased in batches,when the filling level falls below the changing filling level.
 3. Themethod according to claim 2, wherein the increase of the filling levelin batches is made with a single refilling thrust, which refills lessfeedstock than an operating thrust during a normal production operationof the extrusion device.
 4. The method according to claim 2, wherein atleast a volume or a weight of feedstock, which corresponds to thechanging filling level in each feed unit, has a refilling ratio ofbetween 1:1 and 2:1 with at least a volume or a weight of the feedstockof a refilling thrust.
 5. The method according to claim 1, wherein aminimal filling level, which is smaller than the changing filling level,is specified at a defined point in time prior to the end of theproduction order, and the filling level of each feed unit is maintainedabove the minimal filling level for the further production with theextrusion device.
 6. The method according to claim 1, wherein a fillinglevel signal is received by the control device in order to maintain thefilling level.
 7. The method according to claim 2, wherein the fillinglevel of each feed unit is increased in a single refilling thrust, whenthe filling level falls below the changing filling level.
 8. The methodaccording to claim 6, wherein the filling level signal includes at leastone of the following pieces of information: weight of an at leastpartially filled weighing funnel of the respective feed unit, fillinglevel in a weighing funnel of the respective feed unit, filling level ina down pipe of the respective feed unit, and filling level in a feedcontainer of the respective feed unit.